Tropical Storm NADINE (Text)

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TROPICAL STORM NADINE DISCUSSION NUMBER 24
NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012
500 AM AST MON SEP 17 2012
AIRMASS IMAGERY FROM EUMETSAT INDICATES THAT AN UPPER-LEVEL
SHORTWAVE TROUGH IS NOW INTERACTING WITH NADINE...WITH A TONGUE OF
DRY AIR WRAPPING AROUND THE SOUTH AND WEST SIDES OF THE CYCLONE.
THIS HAS RESULTED IN A DECREASE IN THE CENTRAL CONVECTION AND AN
INCREASE IN CONVECTIVE BANDING OVER THE NORTHERN SEMICIRCLE.
SATELLITE INTENSITY ESTIMATES ARE TROPICAL 65 KT FROM TAFB AND
SUBTROPICAL 55-65 KT FROM SAB. A RECENT OSCAT OVERPASS SHOWED
SEVERAL 55 KT WIND VECTORS TO THE SOUTH AND SOUTHEAST OF THE
CENTER...WHILE RECENT CIMSS AMSU INTENSITY ESTIMATES WERE 77-79 KT.
THE INITIAL INTENSITY REMAINS 60 KT BASED ON A BLEND OF THESE DATA.
THE INITIAL MOTION IS NOW 065/15. AN ADDITIONAL REDUCTION IN
FORWARD SPEED AND A TURN TOWARD THE NORTH-NORTHEAST ARE EXPECTED
DURING THE NEXT DAY OR TWO AS A MID-LEVEL RIDGE SLIDES EASTWARD TO
THE NORTH OF NADINE...AND A CUT-OFF LOW FORMS TO THE WEST OF THE
CYCLONE. THE MODEL GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST
48-72 HR...AND THIS PART OF THE NEW FORECAST IS LITTLE CHANGED FROM
THE PREVIOUS ADVISORY. AFTER THAT TIME...ANOTHER MID-/UPPER-LEVEL
LOW IS FORECAST TO MOVE SOUTHWARD OVER THE NORTHEASTERN ATLANTIC
TOWARD NADINE...WITH THE TWO SYSTEMS LIKELY TO STRONGLY INTERACT
AFTER 96 HR. AS THIS OCCURS...THE DYNAMICAL GUIDANCE BECOMES QUITE
DIVERGENT DUE TO THE DIFFERENCES IN HOW THEY DEPICT THIS
INTERACTION. GIVEN THE UNCERTAINTY...THE NEW TRACK FORECAST
FOLLOWS THE TREND OF THE PREVIOUS FORECAST IN SHOWING A SLOW
MOTION...WHICH SMOOTHS THROUGH SOME POSSIBLY VERY ERRATIC MOTION
DURING THIS TIME.
THE GLOBAL MODELS FORECAST THAT NADINE WILL INTERACT WITH THE
CURRENT UPPER-LEVEL TROUGH...AND A SECOND TROUGH APPROACHING FROM
THE WEST...DURING THE NEXT 48 HR. THESE INTERACTIONS SHOULD CAUSE
NADINE TO INGEST UPPER-LEVEL COOL/DRY AIR...WHICH COULD START
EXTRATROPICAL TRANSITION. HOWEVER...THE GLOBAL MODELS AGREE THAT
THERE IS NOT ENOUGH COLD AIR TO COMPLETE TRANSITION...AND THEY
MAINTAIN NADINE AS A WARM-CORE SYSTEM THROUGH AT LEAST 96 HR...
POSSIBLY WITH SOME HYBRID CHARACTERISTICS. THE FORECAST OF NADINE
BECOMING EXTRATROPICAL AT 120 HR IS BASED ON THE PREMISE THAT
INTERACTION WITH THE NORTH ATLANTIC LOW WILL BRING A LARGER BATCH
OF COLD AIR INTO THE SYSTEM. HOWEVER...THIS IS A LOW CONFIDENCE
TRANSITION FORECAST. REGARDLESS OF WHETHER THE CYCLONE IS
TROPICAL...EXTRATROPICAL...OR HYBRID...ALL OF THE INTENSITY
GUIDANCE FORECASTS NADINE TO REMAIN A LARGE AND VIGOROUS SYSTEM
OVER THE NORTHEASTERN ATLANTIC THROUGH THE FORECAST PERIOD.
FORECAST POSITIONS AND MAX WINDS
INIT 17/0900Z 32.0N 36.4W 60 KT 70 MPH
12H 17/1800Z 32.8N 34.7W 55 KT 65 MPH
24H 18/0600Z 34.0N 33.2W 55 KT 65 MPH
36H 18/1800Z 35.2N 32.5W 55 KT 65 MPH
48H 19/0600Z 36.3N 32.2W 55 KT 65 MPH
72H 20/0600Z 37.0N 31.0W 50 KT 60 MPH
96H 21/0600Z 37.0N 29.0W 50 KT 60 MPH
120H 22/0600Z 37.0N 27.0W 50 KT 60 MPH...POST-TROP/EXTRATROP
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FORECASTER BEVEN
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